A surface having a water contact angle equal to or higher than 90° may be generally classified as a hydrophobic or water-repellent surface. The water contact angle on a solid surface may be defined, for example, as a contact angle appearing when a water drop of 3-20 mg is dropped onto the solid surface.
Products having such a water repellent surface may prevent water from penetrating and also show a self-cleaning property because they allow only a small contact area for foreign materials such as dirt or bacteria being placed thereon, which may therefore not be easily attached thereto but readily removed therefrom.
Thanks to such properties, such water repellent products have been widely utilized or under review for their application as water repellent fibers, water repellent coatings, stain-resistant coatings, and anti-corrosion coatings in the fiber industry, the civil engineering and construction industry, the shipbuilding industry, or other mechanical or electronic industries.
The water repellent products are frequently required to have a certain degree of water repellency controlled depending on their application or uses. However, for the water repellent products hitherto produced, controlling their water repellency often turns out to be difficult and thus different water repellent products should be designed for each and every application or use.
Meanwhile, some recent researches have been focused on products having water adhesion properties in conjunction with water repellency. Such types of products may prevent water from penetrating to their solid surface while retaining water thereon and also collect a substantial amount of water on a certain surface area thanks to their water adhesiveness. Based on such characteristics, the products demonstrating both of water repellency and water adhesiveness have been reviewed for their possibilities to be utilized as a water capturing agent or a water capturing device in a region suffering from water shortage.
According to prior arts, however, realization of such products with aforementioned characteristics has inevitably entailed forming an additional fine pattern (e.g., a fine pattern of polydopamine) that demonstrates hydrophilicity and water adhesiveness on a water repellent surface of a substrate such as an anodized aluminum oxide. Practically, such methods are too complicate to be industrially employed, and thus studies regarding the products having both of water repellency and water adhesiveness and industrial applications thereof have faced with major difficulties up to date.